Interobserver Variation in the Interpretation of SSEPs in Anoxic-ischaemic Coma

Objective: To study interobserver variation in the interpretation of median nerve SSEPs in patients with anoxic-ischaemic coma.

Methods: SSEPs of 56 consecutive patients with anoxic-ischaemic coma were interpreted independently by 5 experienced clinical neurophysiologists using guidelines derived from a pilot study. Interobserver agreement was expressed as kappa coefficients.

Results: Kappa ranged from 0.20 to 0.65 (mean 0.52, SD 0.14). Disagreement was related with noise level and failure to adhere strictly to the guidelines in 15 cases. The presence or absence of N13 and cortical peaks caused disagreement in 5 cases each. For recordings with a noise level of 0.25 microV or more, mean kappa was 0.34; for recordings with a noise level below 0.25 microV mean kappa was 0.74.

Conclusions: Interobserver agreement for SSEPs in anoxic-ischaemic coma was only moderate. Since the noise level strongly influenced interobserver variation, utmost attention should be given to its reduction. If an artefact level over 0.25 microV remains, absence of N20 cannot be judged with sufficient certainty and the SSEP should be repeated at a later stage.

Significance: Because of its moderate interobserver agreement, great care has to be given to accurate recording and interpretation of SSEPs before using the recordings for non-treatment decisions.